ABSTRACTThis paper explores the result of

breaking out of the old paradigmconsidered the conventional wisdomof platinum casting - breaking all therules around flask size, type andconfiguration, investment mixturesand de-watering, sprue size and con-figuration, as well as how tall thetree can be and how many pieces canbe cast on a tree.

Using actual examples and photo-graphs, you will learn techniquesthat have proven to work better thanthe old ways. These techniques willinclude “crooked tree” spruing, aspruing technique where the rotationof the casting machine is taken intoconsideration to get maximum fill.

The result is less investmentcracks and resulting finer detail, lesscasting defects, easier de-vesting andhigher yield at lower cost. Thispaper will help you to improve yourplatinum casting ability, as well asyour productivity.

KEYWORDSPlatinum casting, spruing,

investment, tall trees, sprue size,crooked tree, maximum fill, de-vest-ing, technique.

INTRODUCTIONWhen Michael Epstein first

approached me and talked about talltree casting I was very skeptical. Heshowed me a cast tree of platinumeternity rings weighing about 350grams. The one striking feature ofthe tree was the thin center sprue. Itwas only 4.5mm in diameter, yet it

was over six inches tall and support-ed well over 40 rings. During thenext few month, I visited his shopand spent some time with him toexpand and further experiment.Ultimately, casting trees weighing 550grams and holding close to 85 ringswere possible. Many casting experi-ments lead to a whole new under-standing of platinum casting, andbrought about a procedure that isabsolutely amazing.

In this paper I will discuss someof the findings and conclusions thathave been the outcome of these on-going casting experiments.

THE EQUIPMENTThe casting was done with a

Galloni Modular 6 induction castingmachine. This machine develops5KV induction power and was usinga standard coil and 350 gramcapacity crucible.

In later experiments we replacedthe standard induction coil with alarger one (the largest one to fit thismodel casting machine) and used acrucible capable of holding 600grams of platinum.

THE CASTING EXPERIMENTSSeries 1

In the initial casting series, weused a variety of investments, to seeif there are any major advantages ordisadvantages to them. I felt that themore available an investment was,the easier the casting method can beapplied to the industry.

The various investments usedwere Platinum Plus from Ranson &Randolph, Opticast from Kerr, JFormula from Romanoff and WestCast Platinum QC fromRio Grande.

In all cases, the investment prop-erties were changed by reducing thepercentage of the acid that was usedto mix the solution needed to make

the investment by 45% and replacedthe missing portion with distilledwater. That mix was then blendedwith the proper proportions ofdistilled water to create thebinding liquid.

Leaning the acid content createda somewhat more porous investment,which seemed to have the benefitof being more flexible, and allowinggases to escape, withoutsacrificing strength.

In previous experiments, it wasdiscovered that most investmentsare already showing signs of crackingduring the jell state. This hasbeen totally eliminated by theacid modification.

The kiln was at room tempera-ture in some experiments, andat 200°F in others, with nosignificant differences.

Burn-out was done in a comput-erized electric kiln. The alloy castwas Pt950/Iridium.

PREPARING THE FLASKIn these experiments, we used a

3” x 8” perforated flask.The flask was wrapped with 12

layers of “Bounty” brand paper tow-els. In previous trials, it was foundto have the best absorption. Usingmasking tape, the paper towels weresecured around the flask. The perfo-ration of the flask will allow forlateral absorption of the water,which, as you all know, need to beremoved from the flask. This use ofa perforated flask is very unique forcentrifugal casting.

Casting Tree Design and Investment Technique forInduction Platinum CastingJurgen J. Maerz, Director of Technical Education

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THE WAX TREEThrough many experiments we

determined that the ideal diameter ofthe center sprue was to be 4.5mm.In order to make a tall tree, able ofsupporting 40 or more (in laterexperiments as many as 100) rings,this center sprue needed to be sup-ported. The best solution for thiswas a metal core in the center sprue,which would then be removed beforethe actual casting. Using a 1.5 mmcopper wire dipped it into the wax inthe wax pot such a sprue was creat-ed. In later experiments, this copperwire was replaced with silver, asthere was a minor problem with theoxidation of the wire during theburn-out.

The center sprue was then waxedto a wax dome and the wax patternswere attached at a 45 degree angle tothe stem. This is the conventionalmethod used by many casting hous-es. The sprue size of the rings was1 x 2.5mm and was attached to theside of the eternity rings. These ringswere made to support 2-3mm dia-monds. They were ajoured,and drilled.

We were casting four flasks. Tree #1 contained 40 rings. The cen-ter sprue however was 5mm squareand hollow with a 1mm-wall thick-ness. This was done to see if ahollow spruing system was feasibleand economical.

Tree #2 was waxed up with 40eternity rings, sprued at the beforementioned 45 degrees.

Tree #3 contained a wide varietyof small parts, pieces and for a linebracelet and parts of several rings.The unique thing about this tree isthe fact that the wax pieces wereactually distributed over threesprues, coming from the same cone.

Tree # 4 was simply a way to cre-ate some blanks for casting and con-sisted of three wax rods, 8mm indiameter. The resulted cast wire wasthen rolled and used for die strikingother parts in an unrelated manufac-turing sequence.

BURN-OUTThe following schedule was

employed for burn-out.After pouring the investment into

the wrapped flask and additionalvacuuming to remove the air bub-bles, the flask remained on thebench for one hour.

The flask was then set into thekiln and the kiln was brought to200°F within 30 minutes and held atthat temperature for two hours.

After two hours at 200°F thetemperature was brought to 350°Fwith a 1/2 hour ramp.

It remained there for one hour.Then the kiln was opened, the paperand the copper wires were removedfrom the flask and the flask wasplaced back into the kiln. The tem-perature was then ramped up to1700°F in a 3 1/2 hour ramp.

CASTINGFor the casting of these flasks,

the RPM of the machine was sloweddown to the 200-300 range. Oneassumes that when casting platinuma higher speed would bring betterresults. This is not true. At highspeed the metal enters the flask withlots of turbulence. Any suddenchange in direction, any gas obstruc-tion will shorten the distance the liq-uid platinum can flow. By reducingthe speed of the machine, the metalenters in a smooth even flow, has theability to push any gas from insidethe flask away and fill the cavitywith amazing, clean and porousfree castings.

For large pieces the recommend-ed speed of the arm was 200 RPM,for most rings the best results wereobtained at 250 RPM and for a tripletree casting with many small parts,300RPM worked best.

Flask temperature for this experi-ment was at 1700°F. The metaltemperature was set to 1980°C,200°C super heat. The Pt alloywas Pt950/Ir.

RPM for flask #1 and #2 was at250, for flask #3, 300 and for flask#4 at 200.

RESULTAll four flasks filled to the top.

The average weight of each flask was350 grams. The investment wasremoved in a solution of CausticPotash 45%.

Tree #1There were a significant number

of no-fills on the tree. But, if oneconsiders that the center sprue was ahollow one, with a wall thickness ofabout 1mm, then it is amazing thatthe entire tree filled at all. We aban-doned further experiments with hol-low core center sprues. This may besubject of additional research inthe future. Just proving thefeasibility was the goal here.

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Tree #2 There were two no fills at random

position on the leading side of therotation direction. This broughtabout new testing in the next castingrun, experimenting with sprue place-ment and angle.

Tree #3 was filled and again, itshowed some casting flaws on theleading edge in the direction of theflask rotation.

Tree #4 was a complete fill.

All three rods were solid, withalmost no internal porosity.

SERIES 2After several more casting runs

using the technique as describedbefore and observing casting defects,and random no-fills, Michael contin-ued to modify the procedure. Thefirst change was the fact that betterresults were achieved by spruing thewaxes at 90 degrees to the centersprue. Reducing the casting tempera-ture to 1400°F was anotherimprovement. (Actually, somestone-in-place casting using this treemethod was done successfully at500°-600°F-flask temp.)

Experiments with larger items,some weighing as much as one ounce,as well as multi-piece and multi-sprue flasks was being done.

In this casting series the parame-

ters have been changed to includelarger crucible size, the coil on themachine has been replaced to accom-pany this change and the averagecasting tree weighs 550 grams.

The burn-out cycle has been sig-nificantly shortened.

PREPARING THE FLASKThe flasks were again wrapped

with paper towels and taped. Theflask sizes were 3” x 8” and 4” x 6”.

WAXING THE TREEFlask #1

To prove that larger objects canbe cast in the same way, a number offrog design pins were being waxed.Cast, each frog will weigh one ounce.

Flask #2 Another concept was a tree with

several bangle bracelets. It has beensaid that objects of this size are hardto cast. The interesting part on thebracelet tree is the fact that the waxsprues that are making the braceletsare also utilized as sprues for severalrings on the same tree.

Flask #380 eternity rings are on this par-

ticular tree, weighing over 521 gramsonce cast.

Flask #4 four line bracelet partson four separate sprues in one flask.These parts are very small and con-tain the wires that will connectthe bracelet.

THE BURN-OUTFor this experiment, the invest-

ment was R & R Platinum Plus.The Pt alloy was Pt950/Ir as well asPt950/Ru.

After investing, the flasks wereplaced into the kiln without anybench setting time. The kiln was setto come up to 200°F in a one hourramp. After being held at 200°F for1:45 hour (for a 8” x 3”flask) thekiln was brought to the burn-outtemp of 1400°F. This temperaturewas reached within a one-hourramp. After being held at that tem-perature for an additional 1:45 hour,

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the casting was done. It is importantto know that the amount of wax thatis needed to burn as well as the num-ber and size of flasks in that kilnmay extend that time significantly.

CASTING Casting was done using the same

parameters as before. It is importantto note that for the platinumRuthenium alloy the temperaturewas increased by 20°C.

For the larger pieces the RPMwas reduced to 200. The rings werecast at 250RPM and the small pieceswere cast at 300RPM. The flaskswere left to cool until the red wasgone from the button and thendoused in a bucket of water, using ahammer to tap the flask to help withthe investment break-out. After mostof the investment had been removed,the trees were soaked in a heatedsolution of Lye (in this case thebrand name Red Devil) for about 30to 45 minutes.

RESULT Flask #1

All the frogs came out. Because ofa mix-up in the flasks, there was nobutton on this particular castingtree. (The metal for the bangles andthe metal for the frogs were mistak-enly switched). While both treesfilled completely, neither one had abutton.) The castings were smoothwith great detail inside and out.

Flask #2The ring and bangle bracelet tree

filled completely. As above, the lackof a button did not seem to matter.

Flask #3550 grams of eternity rings. The

tree filled to the top. There wereabout seven rings that had fillingproblems along the leading edge ofthe rotation. These problems wereaddressed by further casting experi-ments using a crooked tree. Over all,this 550 gram tree yielded 407 gramsusable product. Almost 75%.

Flask #4This flask too filled all the way

to the top, but there was approxi-mately 10% casting flaws on theleading edge.

This lead to experiments withcrooked casting trees. By adjustingthe angle of the tree in relationshipto the direction of the metal flow andby spruing accordingly, anotherseries of castings were done eachresulting with a complete fill.

CONCLUSION This system of casting has

actually refuted many beliefs regard-ing platinum casting. It proves con-clusively that it is possible to castlarge production trees with a regularinduction machine. It was learnedthat smaller center sprues are betterthan larger ones. The fact that therotation of the casting machine need-

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ed to be slowed down, rather thanspeeded up to get complete fill.Single, small diameter sprues onobjects seem to yield better resultsthan multiple thick sprues.

About the casting quality, I amhappy to say that there was very lit-

tle porosity and that the pieces, espe-cially the eternity rings could beused with very little finishing time.We are currently testing bend flasks,which allow for the flow of the metaland follow the natural path of theplatinum within the flask. The modi-fication of the investments as well asthe spruing technique that followsthe bend stem, allow for a near100% fill every time. There will be

more testing and more refining ofthis technique, but the people thatwere asked to try this and follow thissystem have all reported majorimprovements in their castingresults.

ACKNOWLEDGEMENTS My thanks go to Michael Epstein

of EPS LLC in Feasterville, PA forhis dedication and expert skills todevelop this system, and allowing meto take part in the experimentationand write about it.

-Greg Normandeau who was alwaysaround when I needed some extraadvise.

-Rio Grande and Kerr for providinginvestments to do these experiments.

-PGI for encouraging this research.

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